The present invention relates to a working machine, comprising an engine compartment, an engine hood, an internal combustion engine arranged in the engine compartment and an exhaust system which extends from the engine out of the engine compartment via the engine hood, the exhaust system being provided with an air intake for admitting air from the engine compartment into the exhaust system and entraining the air together with the exhaust gases.
The invention also relates to a method of ventilating the engine compartment of such a working machine.
The term working machine must be regarded as signifying and includes both stationary machines and vehicles. It relates in particular to machines with substantially closed engine compartment in which the temperature can be very high and in which there is a need for ventilation of the engine compartment. Even in vehicles in which the air stream sometimes functions as a ventilator, there will be times, when the vehicle is working but is moving slowly or is stationary, where further ventilation is desirable.
The invention will be described taking a wheel loader as an example of the working machine.
Usually, in conventional wheel loaders, the engine compartment is substantially closed and high operating temperatures therefore occur in the engine compartment.
The prior art solves this problem by providing a combined air and exhaust pipe. This exhaust pipe, which defines a tailpipe of the exhaust system, extends out of the engine compartment from an opening in the engine hood. That is to say, one end of this tailpipe opens into the engine compartment, whilst the other end opens into the atmosphere. An exhaust pipe of the exhaust system extends from the engine compartment into the center of the tailpipe in order to carry the exhaust gases into the tailpipe and via this out into the atmosphere. The outer circumference of the exhaust pipe is smaller than the inner circumference of the tailpipe, so that an annular gap is formed between these pipes. Air from the engine compartment can be led out in this annular gap.
The exhaust pipe opens inside the tailpipe, which in turn means that as they flow the exhaust gases expand to a greater volume, with the result that a certain ejector effect occurs in the area where the exhaust gases flow out of the exhaust pipe and into the tailpipe. The ejector effect or ejector action will contribute and lead to the air in the surrounding, annular gap being entrained by the exhaust gases out through the tailpipe into the surrounding atmosphere.
It is desirable to provide a method and a working machine which will produce more efficient ventilation of an engine compartment than the prior art.
It is desirable to provide such a method and working machine wherein the principle of utilizing the ejector effect to ventilate air out of the engine compartment is used to better effect in comparison to the prior art. An aspect of the present invention proposes a method and a working machine, which in its practical application takes up relatively little space inside the engine compartment and which provides a robust and reliable solution to the problem of ventilating closed or at least substantially closed engine compartments.
According to an aspect of the invention, in a method, air is led in essentially centrally into an outlet duct and the exhaust gases are led into an outlet duct outside, that is to say radially outside, around the air, in such a way that the air is entrained out of the engine compartment by the exhaust gases through an ejector effect that is produced by the exhaust gases.
Leading the air in centrally into an outlet duct, preferably formed by a tailpipe projecting from the engine hood, instead of leading the air into an annular gap surrounding the exhaust pipe, from which the exhaust gases are introduced into the outlet duct, as in the prior art, gives a stronger ejector effect. Compared to the prior art, a larger quantity of air can thereby by entrained by a given quantity of exhaust gases.
According to a preferred embodiment of the invention the air is led into the outlet duct in proximity to an extremely hot and/or temperature-sensitive location in the engine compartment, preferably directly opposite a turbo unit or engine manifold. That is to say air is drawn from a location in the engine compartment where the need for ventilation is greatest.
According to a further aspect of the invention, in a working machine, the air intake comprises an air baffle element which leads the air into an essentially central area in an outlet duct in which the exhaust gases are led out, in such a way that the air is entrained out of the engine compartment by the exhaust gases through an ejector effect which the exhaust gases exert on the air.
According to a preferred embodiment of the invention the air baffle element comprises a pipe which extends into and essentially coaxially with the outlet duct. The term pipe must be regarded as signifying and also includes very short pipes or conduits. The pipe may have a varying wall thickness and also a varying inner and outer radius over its length.
The air baffle element preferably forms an air baffle duct, the cross-section of which diminishes toward the point where it opens into the outlet duct. That is to say, the air baffle element is funnel-shaped. In this way air can be effectively entrained and led into the outlet duct.
The arrangement advantageously comprises means of directing the exhaust gases along an annular gap in the part of the outlet duct where the air baffle element introduces the air. The function of these means, in other words, is to direct the exhaust gases so that these flow in a gap in the outlet duct which precedes a part of the outlet duct where they are permitted to expand to a larger volume together with the air from the air baffle element. The gap should be situated radially outside the air baffle element. In this case the gap need not be continuous in a circumferential direction, although this is preferable. Its cross-sectional area, or flow area, should be so great that it does not generate a resistance to the exhaust gas flow large enough to risk choking the engine. However, its area should not be too large, since this would result in too low an exhaust gas speed and insufficient ejector effect when the gases are permitted to expand in the outlet duct. The outlet duct has a cross-sectional area which is significantly larger than the cross-sectional area of the gap, and which is preferably equal to the sum of the mouth area of the air baffle duct and the gap area.
The means of directing the exhaust gases along an annular gap preferably comprise the outer periphery of the air baffle element.
The outlet duct in which the air baffle element extends is then defined by a wall, which has an inner periphery extending at a constant distance from the outer periphery of the air baffle element in the area where the wall and the air baffle element overlap one another. Air and exhaust gases thereby flow in a parallel direction into the common outlet duct. The air baffle element extends far enough from its engine compartment orifice to avoid a backflow of air (and exhaust gases) into the engine compartment via the air baffle duct of the air baffle element. The flow directions of the exhaust gases and the air as they enter the common part of the outlet duct are also designed to prevent such backflow.
According to a preferred embodiment of the invention the exhaust system comprises a chamber into which the exhaust gases are led via an exhaust pipe connected thereto and into which the air baffle element projects from one direction and from which the outlet duct, into which the air baffle element opens, leads out in an opposite direction. The chamber acts as a collecting chamber, in which the exhaust gases are collected and distributed all around the air baffle element, which projects through the chamber and into the outlet duct.